Re: [PATCH RFC] videobuf2: Improve file I/O emulation to handle buffers in any order

[Hans Verkuil <hverkuil@xs4all.nl>]

Hi Andy,

As I mentioned in irc I have been working in this same area as well, so
I'll take this patch and merge it in my tree and test it as well.

I suspect that it might be easiest if I add the patch to my upcoming
patch series in order to prevent merge conflicts. I'll know more later
today.

Regards,

	Hans

On 11/21/2013 02:05 AM, Andy Walls wrote:
> (This patch is RFC, because it was compiled and tested against kernel
> v3.5)
> 
> videobuf2 file I/O emulation assumed that buffers dequeued from the
> driver would return in the order they were enqueued in the driver. 
> 
> Improve the file I/O emulator's book-keeping to remove this assumption.
> 
> Also remove the, AFAICT, assumption that only read() calls would need to
> dequeue a buffer from the driver.
> 
> Also set the buf->size properly, if a write() dequeues a buffer.
> 
> 
> Signed-off-by: Andy Walls <awalls@md.metrocast.net>
> Cc: Kyungmin Park <kyungmin.park@samsung.com>
> Cc: PawelOsciak<pawel@osciak.com>
> Cc: Marek Szyprowski <m.szyprowski@samsung.com>
> 
> 
> diff --git a/drivers/media/video/videobuf2-core.c b/drivers/media/video/videobuf2-core.c
> index 9d4e9ed..f330aa4 100644
> --- a/drivers/media/video/videobuf2-core.c
> +++ b/drivers/media/video/videobuf2-core.c
> @@ -1796,6 +1796,7 @@ struct vb2_fileio_data {
>  	unsigned int dq_count;
>  	unsigned int flags;
>  };
> +#define FILEIO_INDEX_NOT_SET	((unsigned int) INT_MAX)
>  
>  /**
>   * __vb2_init_fileio() - initialize file io emulator
> @@ -1889,6 +1890,7 @@ static int __vb2_init_fileio(struct vb2_queue *q, int read)
>  				goto err_reqbufs;
>  			fileio->bufs[i].queued = 1;
>  		}
> +		fileio->index = FILEIO_INDEX_NOT_SET;
>  
>  		/*
>  		 * Start streaming.
> @@ -1975,15 +1977,11 @@ static size_t __vb2_perform_fileio(struct vb2_queue *q, char __user *data, size_
>  	 */
>  	q->fileio = NULL;
>  
> -	index = fileio->index;
> -	buf = &fileio->bufs[index];
> -
>  	/*
>  	 * Check if we need to dequeue the buffer.
>  	 */
> -	if (buf->queued) {
> -		struct vb2_buffer *vb;
> -
> +	index = fileio->index;
> +	if (index == FILEIO_INDEX_NOT_SET) {
>  		/*
>  		 * Call vb2_dqbuf to get buffer back.
>  		 */
> @@ -1997,12 +1995,19 @@ static size_t __vb2_perform_fileio(struct vb2_queue *q, char __user *data, size_
>  			goto end;
>  		fileio->dq_count += 1;
>  
> +		fileio->index = fileio->b.index;
> +		index = fileio->index;
> +		buf = &fileio->bufs[index];
> +		
>  		/*
>  		 * Get number of bytes filled by the driver
>  		 */
> -		vb = q->bufs[index];
> -		buf->size = vb2_get_plane_payload(vb, 0);
> +		buf->pos = 0;
>  		buf->queued = 0;
> +		buf->size = read ? vb2_get_plane_payload(q->bufs[index], 0)
> +				 : vb2_plane_size(q->bufs[index], 0);
> +	} else {
> +		buf = &fileio->bufs[index];
>  	}
>  
>  	/*
> @@ -2070,13 +2075,28 @@ static size_t __vb2_perform_fileio(struct vb2_queue *q, char __user *data, size_
>  		 */
>  		buf->pos = 0;
>  		buf->queued = 1;
> -		buf->size = q->bufs[0]->v4l2_planes[0].length;
> +		buf->size = vb2_plane_size(q->bufs[index], 0);
>  		fileio->q_count += 1;
>  
>  		/*
> -		 * Switch to the next buffer
> +		 * Decide on the next buffer
>  		 */
> -		fileio->index = (index + 1) % q->num_buffers;
> +		if (read || (q->num_buffers == 1)) {
> +			/* Use the next buffer the driver provides back */
> +			fileio->index = FILEIO_INDEX_NOT_SET;
> +		} else {
> +			/* Prefer a buffer that is not quequed in the driver */
> +			int initial_index = fileio->index;
> +			fileio->index = FILEIO_INDEX_NOT_SET;
> +			do {
> +				if (++index == q->num_buffers)
> +					index = 0;
> +				if (!fileio->bufs[index].queued) {
> +					fileio->index = index;
> +					break;
> +				}
> +			} while (index != initial_index);
> +		}
>  
>  		/*
>  		 * Start streaming if required.
> 
>